The present invention relates to a plasma processing apparatus to improve the efficiency of utilization of high frequency power by increasing the density of plasma produced between electrodes, which is Utilized as a dry etching apparatus, for example.
Conventionally, the plasma processing apparatuses in which parallel plate electrodes are opposite each other, i.e. opposed electrodes, are provided within a vacuum processing chamber have generally been employed in etching processes for manufacturing semiconductor devices. In particular, with increases in the diameters of wafers, plasma processing apparatuses of a so-called single wafer processing type, in which the wafers are processed one by one, have become popular.
In order to improve the productivity of the plasma processing apparatus of this single wafer processing type, the processing speed thereof must be increased by one figure compared to that of another conventional plasma processing apparatus of a so-called batch processing type in which a large number of wafers are processed at a time.
As a means for increasing the processing speed of plasma processing, a plasma processing apparatus of a so-called narrow gap type has been known in the art as shown in JP-A-62-69620, for example. In this narrow gap type plasma processing apparatus, the gap distance between parallel plate electrodes located opposite each other is selected to be approximately 10 mm. Further, an annular narrow gap constructive member made of insulating material is provided along the peripheral portions of the parallel plate electrodes so that a narrow gap in a range of 1 to 2 mm, which is narrower than the above-described distance of the parallel plate electrodes, is formed along the peripheral portions of the parallel plate electrodes. By the provision of the thus constructed narrow gap, when the high frequency power is applied between the parallel plate electrodes, reactive gas plasma produced between the parallel plate electrodes can be confined in a space between these electrodes inside the narrow gap to thereby increase the density of plasma, so that the efficiency in utilization of the high frequency power is improved and the processing speed is increased (refer to FIG. 4).
FIG. 4 schematically shows a parallel plate electrode unit or an opposed electrode unit provided within the vacuum processing chamber 1 of the conventional dry etching apparatus. The opposed electrode unit includes an electrode 2 to which high frequency power is supplied and another electrode 3 which is provided at the wall portion of the vacuum processing chamber 1 and is biased at the ground potential. An annular narrow gap forming member 19 made of insulating material is arranged along the peripheral portions of the electrodes 2 and 3, so that an narrow gap portion 4 having an interval narrower than that between the central portions of the parallel plate electrodes which are positioned within the narrow gap constructive member is formed.
An insulating member 11 (manufactured, for example, by polytetrafluoroethlene) is provided which covers the outer side surface and also the lower surface of the electrode 2. An ground shield 12 made of conductive material (e.g., aluminum) is provided on the outer side surface and lower surface of the insulating member 11.
The other electrode 3 is provided along the wall portion of the vacuum processing chamber 1 and is biased at the ground potential. A large quantity of small through-holes or bores 14 are formed in the central portion of the electrode 3 so as to penetrate therethrough at an area of the electrode 3 that covers a wafer 5 positioned opposite the electrode 3. A gas reservoir 15 is formed between the electrode 2 and the wall portion of the vacuum processing chamber 1, so that reactive gas (for example, a mixture of CF4 and CHF3) which has been introduced into the gas reservoir 15 through a gas conductive tube 7 can be uniformly introduced into a space 16 sandwiched between the electrodes 2 and 3 and hence also introduced uniformly over the entire surface of the wafer 5.
An annular cover ring 17 made of insulating material is provided at the peripheral portion of the electrode 3 in order to form the narrow gap portion 4 together with the narrow gap forming member 19. A cylindrical ground shield 18 made of conductive material is provided on the outside of the cover ring 17.
According to the plasma processing apparatus having an opposed electrode unit constructed thus as shown in FIG. 4, when the gas is conducted into the space 16 between the electrodes 2 and 3, and high frequency power is applied to the electrode 2, discharge will occur between the electrodes 2 and 3, producing plasma. In this case, since the discharge impedance is high at the portion of the narrow gap forming member 19 made of the insulating material provided at the peripheral portion of the electrode 2, the discharge phenomenon is prevented at the portion of the narrow gap forming member. As a consequence, discharge phenomenon is uniformly concentrated onto the surface of the electrode 2 which is surrounded by the narrow gap forming member 19, whereby the plasma processing operation can be uniformly carried out at high efficiency and at a high speed.
In the conventional narrow gap type plasma processing apparatuses, for example etching apparatuses, a high-speed plasma processing operation can be realized by making the interval between the parallel plate electrodes narrower, increasing the pressure of the gas conducted into the space between the electrodes, and confining the plasma within a region where the wafer is processed.
In the conventional etching apparatuses, the processing precision can be achieved such that the line width is 0.8 micrometers and the aspect ratio is on the order of 1.5. In accordance with the demands for fineness (for instance, line widths of 0.5 micrometers or less and aspect ratios of 2.0 or more) of semiconductor devices, it has been required that pressure in the space between the parallel plate electrodes is lowered (10 Pa or less) to enhance the direct impingement property of particles in the reactive gas plasma which contributes to the processing of the wafer surface. That is, the particles such as ions and active radicals directly impinge on the wafer surface without scattering. However, the above-mentioned narrow gap type plasma processing apparatus has a problem or difficulty in lowering the pressure in the space between the parallel plate electrodes, since the narrow gap portion forms low conductance with respect to exhaust in the space between the electrodes at the central portions thereof, whereby this narrow gap portion would hinder such requirements.
When the narrow gap is designed to be, for instance, 1 mm, even if the vacuum processing chamber is exhausted to achieve internal pressure of approximately 5 Pa, the pressure in the space between the electrodes would be on the order of 40 Pa. Accordingly, the above-mentioned object to enhance the direct impingement property could not be achieved.